LeetCode Problem 2.Add Two Numbers

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

题目说有两个链表分别存储了两个非负整数，链表把数是倒着存的，链表的每个节点只存放一位数字，让你把这两个数加起来然后以题目中的链表形式返回。

举个例子：有两个非负整数342和465，加起来是807，那么在链表中就是2->4->3，5->6->4，返回的807的链表应该是7->0->8。

这个题思路上没难度，就是遍历两个链表，数位分别相加，唯一要注意的地方就是两个数字相加大于10要进位的问题。

代码如下：

 1 class Solution{
 2 public:
 3     ListNode* addToNumbers(ListNode* l1, ListNode* l2){
 4         ListNode* result_list = new ListNode(0);
 5         ListNode* cursor_pointer = result_list;
 6         int carry_num = 0;
 7         while (true){
 8             if (l1 != NULL){
 9                 carry_num += l1->val;
10                 l1 = l1->next;
11             }
12             if (l2 != NULL){
13                 carry_num += l2->val;
14                 l2 = l2->next;
15             }
16             cursor_pointer->val = carry_num % 10;
17             carry_num /= 10;
18             if (l1 != NULL || l2 != NULL || carry_num > 0){
19                 cursor_pointer = (cursor_pointer->next = new ListNode(0));
20             }
21             else{
22                 break;
23             }
24         }
25         return result_list;
26     }
27 };